This invention relates to a process for the production of a controlled-rheology resin of a homopropylene or a propylene copolymer (block copolymer or statistical copolymer) or a polymer composition that comprises a propylene homopolymer or copolymer.
At present, this technique for controlling the rheology of these homopolymers and copolymers consists of a peroxide degradation of the latter, and it is used to develop fluid products in an efficient way without having a detrimental effect in terms of production flow rates by reducing the number of basic polymerization powders.
Thus, various products with fluidity indices that are higher than that of the base are produced from the same polymer or copolymer (generally viscous) by introducing an extrusion peroxide at the outlet of the polymerization reactor. The peroxide is broken down in the extruder to create radicals that themselves will attack the polymer chains by breaking them. In addition, the longest chains preferably will be broken, which involves a reduction of the molecular weights, whereby this reduction of molecular weights is accompanied by a reduction of the distribution of molecular weights ({overscore (M)}w/{overscore (M)}n).
It is also possible to melt a propylene homopolymer or copolymer powder or a polymer composition powder that comprises such a propylene homopolymer or copolymer and to incorporate in it a peroxide (repeat synthesis) for the purpose of extrusion followed by granulation.
The drawback of this process resides in the fact that these products have mechanical properties: strength and shock resistance, that are weaker than a product that is obtained directly after polymerization, extrusion and granulation or than a powder that was again subjected to extrusion and to granulation.
Documents that illustrate the prior art are: WO-A-96/12753; EP-A-570 812; U.S. Pat. No. 5,932,660; JP-A-07/138 320; U.S. Pat. No. 5,530,073; WO-A-96/06872; U.S. Pat. No. 5,705,568; U.S. Pat. No. 3,862,265; U.S. Pat. No. 5,945,492; CA-A-2 258 305; U.S. Pat. No. 4,900,781; DE-A-1 694 563; U.S. Pat. No. 4,672,088; and EP-A-0 853 090.
Seeking to solve this problem, the applicant company discovered, surprisingly enough, that by incorporating, instead of the peroxides of the prior art or in addition to the latter, stable free radicals into the resins that are to be modified, placed in a viscous state (in a molten zone of an extruder or in solvent medium), the desired resins that therefore have a higher fluidity index and better mechanical properties are obtained with the following additional advantages:
Incorporation of stable radicals that are always present after extrusion provides a better thermal stability to the products that are obtained, improves the UV resistance of the latter and reduces their tendency to depolymerize; and
in the case where a peroxide is also incorporated into the resin, the latter has a more stable viscosity over time because of comprising a reservoir of heat-reacting counter-radicals. Actually, a polypropylene-type resin that is degraded by a peroxide may contain peroxide radicals. The presence of this peroxide runs the risk of modifying the viscosity of the resin when the latter is transformed (when hot), whereby during this transformation, the peroxide again plays its resin-degrading role to reduce its viscosity. Now, during storage, the peroxide has the tendency to migrate and therefore to leave the resin, and, during the storage period, the resin may therefore have a different behavior and show a viscosity that is different during or after transformation, depending on whether there is a little or a lot of peroxide. According to the process of this invention, however, the resin contains a reservoir with stable free radicals that have the tendency to neutralize the peroxide as soon as the latter is broken down, thus reducing its degradation effects, regardless of whether its concentration is high or low. The storage period thus no longer has as much effect on the viscosity of the transformed resin.
This invention relates to a process for the production of a controlled-rheology resin of a propylene homopolymer or copolymer or a composition that comprises a propylene homopolymer or copolymer, characterized by the fact that at least one stable free radical is incorporated into said resin in the viscous state in an amount that can increase the fluidity index of said resin, since a solid product that has an increased fluidity index is formed. This phrase means that the stable free radical does not prevent the fluidity index of the resin from increasing during the process of the invention, even if by itself, the stable free radical may sometimes tend to limit the extent of this increase. In any case, the process according to the invention leads to a resin with a fluidity index that is increased relative to the starting resin under the action of cuts of polymer chains, whereby said cuts take place under the action of heat and/or under the action of polymerization triggers. A polymerization trigger is defined as a free radical initiator that can bring about the cuts of polymer chains (no polymerization takes place during the process of the invention).
This invention therefore has as its object a process for the production of a controlled-rheology resin of a propylene homopolymer or copolymer or a composition that comprises a propylene homopolymer or copolymer in the absence of a functional monomer, whereby said process brings about an increase in the fluidity index of the resin by cuts of chains, characterized by the fact that at least one stable free radical is incorporated into said resin in the viscous state, since a solid product that has an increased fluidity index is formed.
The stable free radical or radicals is or are selected in particular from among the nitroxide radicals, i.e. that contain the xe2x95x90Nxe2x80x94Oxe2x80x2 group, in particular from among those of formulas (Ia), (Ib) or (Ic): 
in which:
R1 to R3, R5 to R8, and R13 and R14 each represent independently:
(a) a hydrogen atom;
(b) a halogen atom, such as chlorine, bromine, or iodine;
(c) a hydrocarbon-containing, saturated or unsaturated, linear, branched or monocyclic or polycyclic group that can be substituted by at least one halogen;
(d) an ester group xe2x80x94COOR15 or an alkoxyl group xe2x80x94OR16, R15 and R16 that represent a hydrocarbon-containing group as defined in item (c) above;
(e) a group of formula 
where R17 and R18 each independently represent a linear, branched or cyclic alkyl radical, a perfluoroalkyl radical, aryl radical, aralkyl, radical, alkaryl radical, alkoxyl radical, aryloxyl radical, aralkyloxyl radical, alkaryloxy radical, whereby these radicals can comprise 1 to 20 carbon atoms; or halogen such as chlorine, bromine, fluorine or iodine;
(f) a polymer chain that can be, for example, a poly(alkyl methacrylate) chain or a poly(alkyl acrylate) chain, such as poly(methyl methacrylate), polydiene such as polybutadiene, polyolefins such as polyethylene or polybutadiene, but that is preferably a polystyrene chain;
R4 has the meanings that are defined in items (a), (b), (c), (d) and (f) above, and in the case where it is connected to the nitrogen atom by a carbon atom, the latter can carry at least one group as defined in item (e) above;
R9 to R12, identical or different, have the meanings that are defined in items (a) to (f) above and can also represent a hydroxide group or an acid group, such as xe2x80x94COOH, xe2x80x94PO(OH)2 or xe2x80x94SO3H;
R3 and R4 can be connected to one anotherxe2x80x94in the case where R4 represents a radical xe2x80x94CRxe2x80x21Rxe2x80x22Rxe2x80x23 (whereby Rxe2x80x21 to Rxe2x80x23 equally have the meanings of R1 to R3); and R3 can be connected to Rxe2x80x23xe2x80x94to form a heterocycle that
comprises the nitrogen atom of 
whereby said
heterocycle can be saturated or unsaturated, can comprise in the cycle at least one other heteroatom and/or at least one group 
and can also comprise a cycle that is attached, saturated or unsaturated;
two from among R1 to R3, R5 and R6, R7 and R8, R9 and R10, R11 and R12, R6 and R9, R8 and R11, R13 and R14 andxe2x80x94in the case where R4 represents a radical xe2x80x94CRxe2x80x21Rxe2x80x22Rxe2x80x23, R3 and Rxe2x80x23xe2x80x94can be connected independently to one another to form, with the carbon atom that carries them, a saturated or unsaturated cycle or heterocyle;
u is a non-zero integer, for example from 1 to 18.
As examples of hydrocarbon-containing groups as defined in item (c) above, it is possible to cite those that have 1 to 20 carbon atoms, such as the linear, branched or cyclic alkyl radicals, and the aryl radicals such as phenyl or naphthyl, and the radicals that comprise at least one aromatic cycle that can be substituted by, for example, a C1-C4 alkyl radical, such as the aralkyl radicals, such as benzyl.
It is possible to mention in particular the nitroxide radicals of formula (Ia) in which one among R2 to R3 has a molecular weight that is greater than 15, preferably greater than 30, in particular between 40 and 450.
A particular family of the nitroxide radicals that can be considered according to this invention is that of the nitroxide radicals of formula (Ia), in which R3 and R4 (or R3 and Rxe2x80x23) are connected to one another and that are selected in particular from among: 
where:
Ra to Rk and Rm independently have the meanings that are given for R9 to R12, whereby Ra and Rb and Re and Rf can be identical or different when they are carried by different carbon atoms;
r is equal to 2 or 3 or 4;
s is a non-zero integer, in particular from 1 to 10;
t is equal to 0, 1 or 2.
Furthermore, as particular examples of nitroxide radicals, the following can be indicated:
2,2,5,5 Tetramethyl-1-pyrrolidinyloxy (generally marketing under the trademark PROXYL): 
3-carboxy-2,2,5,5-tetramethyl-pyrrolidinyloxy (commonly called 3-carboxy PROXYL);
2,2,6,6-tetramethyl-1-piperidinyloxy (commonly called TEMPO): 
4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (commonly called 4-hydroxy-TEMPO);
4-methoxy-2,2,6,6-tetramethyl-1-piperidinyloxy (commonly called 4-methoxy-TEMPO);
4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy (commonly called 4-oxo-TEMPO;
bis-(1-oxyl-2,2,6,6-tetramethylpiperidine-4-yl)sebacate, represented by the formula: 
(marketed under the trademark xe2x80x9cCXA 5415xe2x80x9d by the xe2x80x9cCIBA SPECIALTY CHEMICALxe2x80x9d Company);
2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl)monophosphonate: 
N-tert-butyl-1-diethylphosphono-2,2-dimethyl propyl nitroxide (DEPN): 
N-tert-butyl-1-dibenzylphosphono-2,2-dimethyl propyl nitroxide;
N-tert-butyl-1-di(2,2,2-trifluoroethyl)phosphono-2,2-dimethyl propyl nitroxide;
N-tert-butyl-[(1-diethylphosphono)-2-methyl-propyl]nitroxide;
N-(1-methylethyl)-1-cyclohexyl-1-(diethylphosphono)nitroxide: 
N-(1-phenylbenzyl)-[(1-diethylphosphono)-1-methyl ethyl]nitroxide: 
N-phenyl-1-diethylphosphono-2,2-dimethyl propyl nitroxide;
N-phenyl-1-diethylphosphono-1-methyl ethyl nitroxide;
N-(1-phenyl 2-methyl propyl)-1-diethylphosphono-1-methyl ethyl nitroxide;
N-tert-butyl-1-phenyl-2-methyl propyl nitroxide: 
N-tert-butyl-1-(2-naphthyl)-2-methyl propyl nitroxide.
It is also possible to cite 2,4,6-tri-tert-butyl phenoxy as a non-nitroxide stable radical.
It is possible to incorporate into the resin in the viscous state from 1 ppm to 5% by weight, in particular 10 ppm to 5% by weight, of at least one stable free radical relative to said resin.
Furthermore, according to a particular characteristic of this invention, at least one radical-type polymerization trigger is incorporated into the resin in the viscous state in an amount that is adequate to obtain, after reaction, the resin with the desired viscosity. The value of this viscosity is expressed by MFI, in g/10 minutes.
The radical-type polymerization triggers that can be used are all those that are known to one skilled in the art. It is possible to cite diacyl peroxides, peroxyesters, peroxyketals, dialkyl peroxides, hydroperoxides, peroxydicarbonates, azo compounds and peroxyphthalides.
In particular, it is possible to cite, by way of examples, the radical-type polymerization triggers, from among:
Benzoyl peroxide;
lauroyl peroxide;
decanoyl peroxide;
3,5,5-trimethylhexanoyl peroxide;
acetyl peroxide and sulfonyl cyclohexyl;
tert-butyl peroxybenzoate;
tert-butyl peroxyacetate;
tert-butyl peroxy-3,5,5-trimethylhexanoate;
tert-amyl peroxy-3,5,5-trimethylhexanoate;
2,5-dimethyl-2,5-di(benzoylperoxy)hexane;
OO-tert-butyl-O-isopropyl-monoperoxy carbonate;
OO-tert-butyl-O-(2-ethylhexyl)monoperoxy carbonate;
OO-tert-amyl-O-(2-ethylhexyl)monoperoxy carbonate;
tert-butyl peroxyisobutyrate;
tert-butyl peroxy-2-ethylhexanoate;
tert-amyl peroxy-2-ethylhexanoate;
2,5-dimethyl-2,5-di(2-ethylhexanoyl peroxy)hexane;
tert-butyl peroxypivalate;
tert-amyl peroxypivalate;
tert-butyl peroxyneodecanoate;
tert-butyl peroxyisononanoate;
tert-amyl peroxyneodecanoate;
xcex1-cumyl peroxyneodecanoate;
3-hydroxy-1,1-dimethylbutyl-peroxyneodecanoate;
tert-butyl peroxymaleate;
ethyl 3,3-di(tert-butylperoxy)butyrate;
ethyl 3,3-di(tert-amylperoxy)butyrate;
n-butyl 4,4-di(tert-butylperoxy)valerate;
2,2-di(tert-butylperoxy)butane;
1,1-di(tert-butylperoxy)cyclohexane;
1,1-di(tert-butylperoxy)cyclohexane;
1,1-di(tert-butylperoxy)3,3,5-trimethylcyclohexane;
1,1-di(tert-amylperoxy)cyclohexane;
2,2-bis-(4,4-ditert-butyl peroxy cyclohexyl)propane);
2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-(3);
di-tert-butyl peroxide;
di-tert-amyl peroxide;
tert-butyl peroxide and cumyl peroxide;
1,3-di(tert-butylperoxy-isopropyl)-benzene;
2,5-dimethyl-2,5-di(tert-butylperoxy)hexane;
1,1,4,4,7,7-hexamethylcyclo-4,7-diperoxynonane;
3,3,6,6,9,9-hexamethylcyclo-1,2,4,5-tetraoxa-nonane;
tert-butyl hydroperoxide;
tert-amyl hydroperoxide;
cumyl hydroperoxide;
2,5 dimethyl-2,5-di(hydroperoxy)hexane;
diisopropylbenzene mono hydroperoxide;
paramethane hydroperoxide;
di-(2-ethylhexyl)peroxydicarbonate;
dicyclohexyl peroxydicarbonate;
2,2xe2x80x2-azo-di(2-acetoxypropane);
2,2xe2x80x2-azobis(isobutyronitrile);
2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile);
2,2xe2x80x2-azobis(cyclohexanenitrile);
2,2xe2x80x2-azobis-(2-methylbutyronitrile) and
2,2xe2x80x2-azobis(2,4-dimethyl-4-methoxyvaleronitrile); and
3-phenyl-3-tert-butyl-peroxyphthalide.
It is possible to incorporate the radical-type polymerization triggers in an amount that ranges up to 5% by weight, in particular at a rate of 50 ppm to 0.5% by weight, relative to the weight of the resin.
Furthermore, it is possible to use an SFRxc2x7FSFR/AMOxc2x7FAMO ratio of 0.0001 to 2.5, in particular 0.005 to 2.5, with:
SFR representing the stable free radical mole number in the medium;
FSFR representing the functionality of the stable free radical, i.e., the number of sites on the same stable free radical molecule that exhibits the stable free radical state;
AMO representing the trigger mole number in the medium;
FAMO representing the functionality of the trigger, i.e., the number of sites that exhibit the free radical state that each trigger molecule is capable of generating. The starting resin is in particular a propylene homopolymer.
It is possible to mention all of the possible propylene homopolymers: isotactic polypropylene, atactic polypropylene, syndiotactic polypropylene.
The starting resin can also be a copolymer of the statistical or block propylene, whereby the comonomer or comonomers represent(s) up to 10% by weight of said copolymer. The comonomer or comonomers are selected in particular from among alkylenes, such as ethylene and butylene, dienes, and vinylaromatic monomers, such as styrene. It is possible to cite, by way of examples, the alkylene/propylene copolymers, such as ethylene-propylene block and statistical copolymers, and terpolymers such as alkylene/propylene/butylene, like the ethylene/propylene/butylene terpolymers; monomer propylene/diene copolymers; and styrene-propylene copolymers.
It is also possible to cite, as a starting resin, a propylene homopolymer or a propylene copolymer as defined above mixed with at least one other polymer that is selected in particular from among polyethylene, polystyrene, poly(methyl methacrylate), polybutadiene, an EPDM (monomer ethylene-propylene-diene copolymer), an ethylene-acrylate copolymer, an ethylene-acrylic acid copolymer, an ethylene-acrylate-maleic anhydride terpolymer.
In such a mixture, the other polymer or polymers generally represent at most 50% by weight of the mixture.
It is further specified that the basic resin contains little (less than 200 ppm) or no functional monomer such as maleic anhydride and other functional monomers that comprise the carboxylic acid groups and their derivatives, acid chlorides, isocyanates, oxazolines, epoxides, amines or hydroxides, of which examples are given in U.S. Pat. No. 5,705,563.
According to a first embodiment of the process according to the invention, the stable free radical or radicals, and, if necessary, the trigger or triggers, are introduced into at least one molten zone of the extruder located at the outlet of the reactor for synthesis of the propylene homopolymer or copolymer, or into at least one molten zone of the extruder that is used for repeat synthesis of the propylene homopolymer or copolymer, or else into another extruder that is not necessarily found at the outlet of the polymerization reactor, in which case all of the products that are to be incorporated into the formulation are fed into the extruder.
The resin in the viscous state and the stable radical or stable radicals, and, if necessary, the radical-type polymerization trigger or triggers, and, if necessary, one other polymer or polymers are then brought into contact generally at a temperature of 100xc2x0 C. to 350xc2x0 C., in particular at a temperature of 160xc2x0 C. to 250xc2x0 C., and generally for a period of 10 seconds to 5 hours, preferably for a period of 10 seconds to 1 hour, and, in particular, 15 seconds to 1 minute.
Advantageously, it is possible to introduce the stable free radical or radicals and, if necessary, the trigger or triggers, in solution in a solvent, such as trichlorobenzene, whereby the concentration of the stable free radical or radicals is 1 to 100% by weight (100% corresponding to the absence of solvent). For example, this solution of the stable radical or radicals, and, if necessary, the trigger or triggers, is introduced at an injection flow rate of 0.01-5% by weight of the total flow rate. This solvent, which makes the flow rate exact, is eliminated during the extrusion into degassing wells.
It is also possible to incorporate the stable free radical or radicals, and, if necessary, the trigger or triggers, via a master-batch, such as a mixture of polypropylene or polyethylene powder.
The modified resin according to the process of this invention leaves the extruder in the form of a rod, which is then directed in a known way to a granulation device.
According to a second embodiment of the process according to the invention, the stable radical or radicals, and, if necessary, the polymerization trigger or triggers, are introduced into the starting resin that is placed in the solvent medium at a temperature of 80xc2x0 C. to 350xc2x0 C. The solvent is selected in particular from among the aliphatic, cycloaliphatic and aromatic hydrocarbons, and, if necessary, halogenated (chlorinated) hydrocarbons.
The resin, the stable free radical or radicals, and, if necessary, the trigger or triggers in the presence of solvent are introduced into a reactor, such as a polymerization reactor, and the unit is brought to the desired temperature. This temperature is selected based on the components that are introduced (stable free radicals and triggers). The reaction time is also determined based on the trigger: this reaction time is selected between 3 and 10 half-lives of the trigger at the reaction temperature. After the reaction, the reaction mixture is purified, for example by introduction of the latter via a gear pump into a devolatizer to eliminate the solvent. The molten polymer is then also introduced via a gear pump into a die, followed by a granulator, to obtain granules of the final resin.
With regard to the solvents, it is possible to use all of the solvents of the polyolefins.
Furthermore, in a general manner, a trigger is preferably present for a temperature that is lower than 200xc2x0 C. It is not possible to have a trigger above 200xc2x0 C. there.
In the absence of a trigger, the degradation takes place by cuts of the chain by a radical-type mechanism under the action of heat alone (so-called xe2x80x9cbeta-scissionxe2x80x9d mechanism).
The following examples illustrate this invention without, however, limiting its scope. In these examples:
The percentages are by weight unless otherwise indicated;
the values of fluidity indices IF (Melt Index) have been measured at 230xc2x0 C., below 2.16 kg, according to ISO Standard 1133:91;
the values of the mean molecular weights by number ({overscore (Mn)}) and mean molecular weights by weight ({overscore (M)}) have been measured by GPC;
the values of the modulus were measured on 80xc3x9710xc3x974 specimens, according to ISO Standard 178:93;
the notched Charpy impact tests were carried out at 23xc2x0 C. on 80xc3x9710xc3x974 specimens, according to ISO Standard 179-1eA;
the high-speed impact tests or xe2x80x9cFWIxe2x80x9d were carried out on a 100xc3x97100xc3x972 plate with a speed of the impact separator of 4.3 m/second.
Furthermore, the following abbreviations were used:
HomoPP: Propylene homopolymer that exhibits the following characteristics:
Fluidity index (2.16 kg, 230xc2x0 C.): 3 g/10 minutes
Density: 0.905 g/cm3 
Melting point: 163xc2x0 C.
{overscore (Mn)}=52 200
{overscore (Mw)}=296 200
Ip (polymolecularity index {overscore (Mw)}/{overscore (Mn)})=5.7
Modulus: 1256 MPa
Notched Charpy impact: 3.1 kJ/m2.
PPcopo: copolymer with propylene/ethylene blocks that exhibit the following characteristics:
Fluidity index (2.16 kg, 230xc2x0 C.): 1 g/10 minutes
Density: 0.902 g/cm3 
Melting point: 163xc2x0 C.
Flexural modulus: 1200 MPa
High-speed impact: 80 kJ/m2.
TEMPO: 2,2,6,6-Tetramethyl-1 piperidinyloxy (C9H18NO), with molecular weight 156.25 and melting point 38xc2x0 C.
TEMPOL: (4-Hydroxy-TEMPO)=4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy
DHBP: 2,5-Bis-(tert-butylperoxy)-2,5-dimethyl-hexane, of a developed formula: 
with molecular weight 290.4, in liquid form,
with a purity that is equal to 92%.